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[mlir][spirv] Support poison index when converting vector.insert/extract #125560

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Merged
merged 1 commit into from
Feb 5, 2025
Merged

[mlir][spirv] Support poison index when converting vector.insert/extract #125560

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77 changes: 64 additions & 13 deletions mlir/lib/Conversion/VectorToSPIRV/VectorToSPIRV.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -137,6 +137,33 @@ struct VectorBroadcastConvert final
}
};

// SPIR-V does not have a concept of a poison index for certain instructions,
// which creates a UB hazard when lowering from otherwise equivalent Vector
// dialect instructions, because this index will be considered out-of-bounds.
// To avoid this, this function implements a dynamic sanitization that returns
// some arbitrary safe index. For power-of-two vector sizes, this uses a bitmask
// (presumably more efficient), and otherwise index 0 (always in-bounds).
static Value sanitizeDynamicIndex(ConversionPatternRewriter &rewriter,
Location loc, Value dynamicIndex,
int64_t kPoisonIndex, unsigned vectorSize) {
if (llvm::isPowerOf2_32(vectorSize)) {
Value inBoundsMask = rewriter.create<spirv::ConstantOp>(
loc, dynamicIndex.getType(),
rewriter.getIntegerAttr(dynamicIndex.getType(), vectorSize - 1));
return rewriter.create<spirv::BitwiseAndOp>(loc, dynamicIndex,
inBoundsMask);
}
Value poisonIndex = rewriter.create<spirv::ConstantOp>(
loc, dynamicIndex.getType(),
rewriter.getIntegerAttr(dynamicIndex.getType(), kPoisonIndex));
Value cmpResult =
rewriter.create<spirv::IEqualOp>(loc, dynamicIndex, poisonIndex);
return rewriter.create<spirv::SelectOp>(
loc, cmpResult,
spirv::ConstantOp::getZero(dynamicIndex.getType(), loc, rewriter),
dynamicIndex);
}

struct VectorExtractOpConvert final
: public OpConversionPattern<vector::ExtractOp> {
using OpConversionPattern::OpConversionPattern;
Expand All @@ -154,14 +181,26 @@ struct VectorExtractOpConvert final
}

if (std::optional<int64_t> id =
getConstantIntValue(extractOp.getMixedPosition()[0]))
rewriter.replaceOpWithNewOp<spirv::CompositeExtractOp>(
extractOp, dstType, adaptor.getVector(),
rewriter.getI32ArrayAttr(id.value()));
else
getConstantIntValue(extractOp.getMixedPosition()[0])) {
// TODO: ExtractOp::fold() already can fold a static poison index to
// ub.poison; remove this once ub.poison can be converted to SPIR-V.
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(I intend to tackle ub.poison to SPIR-V conversion myself soon, and I'll clean this up in that commit.)

if (id == vector::ExtractOp::kPoisonIndex) {
// Arbitrary choice of poison result, intended to stick out.
Value zero =
spirv::ConstantOp::getZero(dstType, extractOp.getLoc(), rewriter);
rewriter.replaceOp(extractOp, zero);
} else
rewriter.replaceOpWithNewOp<spirv::CompositeExtractOp>(
extractOp, dstType, adaptor.getVector(),
rewriter.getI32ArrayAttr(id.value()));
} else {
Value sanitizedIndex = sanitizeDynamicIndex(
rewriter, extractOp.getLoc(), adaptor.getDynamicPosition()[0],
vector::ExtractOp::kPoisonIndex,
extractOp.getSourceVectorType().getNumElements());
rewriter.replaceOpWithNewOp<spirv::VectorExtractDynamicOp>(
extractOp, dstType, adaptor.getVector(),
adaptor.getDynamicPosition()[0]);
extractOp, dstType, adaptor.getVector(), sanitizedIndex);
}
return success();
}
};
Expand Down Expand Up @@ -266,13 +305,25 @@ struct VectorInsertOpConvert final
}

if (std::optional<int64_t> id =
getConstantIntValue(insertOp.getMixedPosition()[0]))
rewriter.replaceOpWithNewOp<spirv::CompositeInsertOp>(
insertOp, adaptor.getSource(), adaptor.getDest(), id.value());
else
getConstantIntValue(insertOp.getMixedPosition()[0])) {
// TODO: ExtractOp::fold() already can fold a static poison index to
// ub.poison; remove this once ub.poison can be converted to SPIR-V.
if (id == vector::InsertOp::kPoisonIndex) {
// Arbitrary choice of poison result, intended to stick out.
Value zero = spirv::ConstantOp::getZero(insertOp.getDestVectorType(),
insertOp.getLoc(), rewriter);
rewriter.replaceOp(insertOp, zero);
} else
rewriter.replaceOpWithNewOp<spirv::CompositeInsertOp>(
insertOp, adaptor.getSource(), adaptor.getDest(), id.value());
} else {
Value sanitizedIndex = sanitizeDynamicIndex(
rewriter, insertOp.getLoc(), adaptor.getDynamicPosition()[0],
vector::InsertOp::kPoisonIndex,
insertOp.getDestVectorType().getNumElements());
rewriter.replaceOpWithNewOp<spirv::VectorInsertDynamicOp>(
insertOp, insertOp.getDest(), adaptor.getSource(),
adaptor.getDynamicPosition()[0]);
insertOp, insertOp.getDest(), adaptor.getSource(), sanitizedIndex);
}
return success();
}
};
Expand Down
47 changes: 43 additions & 4 deletions mlir/test/Conversion/VectorToSPIRV/vector-to-spirv.mlir
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Original file line number Diff line number Diff line change
Expand Up @@ -176,7 +176,8 @@ func.func @extract(%arg0 : vector<2xf32>) -> (vector<1xf32>, f32) {
// -----

func.func @extract_poison_idx(%arg0 : vector<4xf32>) -> f32 {
// expected-error@+1 {{index -1 out of bounds for 'vector<4xf32>'}}
// CHECK: %[[ZERO:.+]] = spirv.Constant 0.000000e+00
// CHECK: return %[[ZERO]]
%0 = vector.extract %arg0[-1] : f32 from vector<4xf32>
return %0: f32
}
Expand Down Expand Up @@ -208,12 +209,31 @@ func.func @extract_size1_vector_dynamic(%arg0 : vector<1xf32>, %id : index) -> f
// CHECK-LABEL: @extract_dynamic
// CHECK-SAME: %[[V:.*]]: vector<4xf32>, %[[ARG1:.*]]: index
// CHECK: %[[ID:.+]] = builtin.unrealized_conversion_cast %[[ARG1]] : index to i32
// CHECK: spirv.VectorExtractDynamic %[[V]][%[[ID]]] : vector<4xf32>, i32
// CHECK: %[[MASK:.+]] = spirv.Constant 3 :
// CHECK: %[[MASKED:.+]] = spirv.BitwiseAnd %[[ID]], %[[MASK]] :
// CHECK: spirv.VectorExtractDynamic %[[V]][%[[MASKED]]] : vector<4xf32>, i32
func.func @extract_dynamic(%arg0 : vector<4xf32>, %id : index) -> f32 {
%0 = vector.extract %arg0[%id] : f32 from vector<4xf32>
return %0: f32
}

// -----

// CHECK-LABEL: @extract_dynamic_non_pow2
// CHECK-SAME: %[[V:.*]]: vector<3xf32>, %[[ARG1:.*]]: index
// CHECK: %[[ID:.+]] = builtin.unrealized_conversion_cast %[[ARG1]] : index to i32
// CHECK: %[[POISON:.+]] = spirv.Constant -1 :
// CHECK: %[[CMP:.+]] = spirv.IEqual %[[ID]], %[[POISON]]
// CHECK: %[[ZERO:.+]] = spirv.Constant 0 :
// CHECK: %[[SELECT:.+]] = spirv.Select %[[CMP]], %[[ZERO]], %[[ID]] :
// CHECK: spirv.VectorExtractDynamic %[[V]][%[[SELECT]]] : vector<3xf32>, i32
func.func @extract_dynamic_non_pow2(%arg0 : vector<3xf32>, %id : index) -> f32 {
%0 = vector.extract %arg0[%id] : f32 from vector<3xf32>
return %0: f32
}

// -----

// CHECK-LABEL: @extract_dynamic_cst
// CHECK-SAME: %[[V:.*]]: vector<4xf32>
// CHECK: spirv.CompositeExtract %[[V]][1 : i32] : vector<4xf32>
Expand Down Expand Up @@ -264,8 +284,10 @@ func.func @insert(%arg0 : vector<4xf32>, %arg1: f32) -> vector<4xf32> {

// -----

// CHECK-LABEL: @insert_poison_idx
// CHECK: %[[ZERO:.+]] = spirv.Constant dense<0.000000e+00>
// CHECK: return %[[ZERO]]
func.func @insert_poison_idx(%arg0 : vector<4xf32>, %arg1: f32) -> vector<4xf32> {
// expected-error@+1 {{index -1 out of bounds for 'vector<4xf32>'}}
%1 = vector.insert %arg1, %arg0[-1] : f32 into vector<4xf32>
return %1: vector<4xf32>
}
Expand Down Expand Up @@ -306,14 +328,31 @@ func.func @insert_size1_vector_dynamic(%arg0 : vector<1xf32>, %arg1: f32, %id :
// CHECK-LABEL: @insert_dynamic
// CHECK-SAME: %[[VAL:.*]]: f32, %[[V:.*]]: vector<4xf32>, %[[ARG2:.*]]: index
// CHECK: %[[ID:.+]] = builtin.unrealized_conversion_cast %[[ARG2]] : index to i32
// CHECK: spirv.VectorInsertDynamic %[[VAL]], %[[V]][%[[ID]]] : vector<4xf32>, i32
// CHECK: %[[MASK:.+]] = spirv.Constant 3 :
// CHECK: %[[MASKED:.+]] = spirv.BitwiseAnd %[[ID]], %[[MASK]] :
// CHECK: spirv.VectorInsertDynamic %[[VAL]], %[[V]][%[[MASKED]]] : vector<4xf32>, i32
func.func @insert_dynamic(%val: f32, %arg0 : vector<4xf32>, %id : index) -> vector<4xf32> {
%0 = vector.insert %val, %arg0[%id] : f32 into vector<4xf32>
return %0: vector<4xf32>
}

// -----

// CHECK-LABEL: @insert_dynamic_non_pow2
// CHECK-SAME: %[[VAL:.*]]: f32, %[[V:.*]]: vector<3xf32>, %[[ARG2:.*]]: index
// CHECK: %[[ID:.+]] = builtin.unrealized_conversion_cast %[[ARG2]] : index to i32
// CHECK: %[[POISON:.+]] = spirv.Constant -1 :
// CHECK: %[[CMP:.+]] = spirv.IEqual %[[ID]], %[[POISON]]
// CHECK: %[[ZERO:.+]] = spirv.Constant 0 :
// CHECK: %[[SELECT:.+]] = spirv.Select %[[CMP]], %[[ZERO]], %[[ID]] :
// CHECK: spirv.VectorInsertDynamic %[[VAL]], %[[V]][%[[SELECT]]] : vector<3xf32>, i32
func.func @insert_dynamic_non_pow2(%val: f32, %arg0 : vector<3xf32>, %id : index) -> vector<3xf32> {
%0 = vector.insert %val, %arg0[%id] : f32 into vector<3xf32>
return %0: vector<3xf32>
}

// -----

// CHECK-LABEL: @insert_dynamic_cst
// CHECK-SAME: %[[VAL:.*]]: f32, %[[V:.*]]: vector<4xf32>
// CHECK: spirv.CompositeInsert %[[VAL]], %[[V]][2 : i32] : f32 into vector<4xf32>
Expand Down